1 //== TestAfterDivZeroChecker.cpp - Test after division by zero checker --*--==//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This defines TestAfterDivZeroChecker, a builtin check that performs checks
10 // for division by zero where the division occurs before comparison with zero.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
16 #include "clang/StaticAnalyzer/Core/Checker.h"
17 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 #include "llvm/ADT/FoldingSet.h"
20 #include <optional>
21
22 using namespace clang;
23 using namespace ento;
24
25 namespace {
26
27 class ZeroState {
28 private:
29 SymbolRef ZeroSymbol;
30 unsigned BlockID;
31 const StackFrameContext *SFC;
32
33 public:
ZeroState(SymbolRef S,unsigned B,const StackFrameContext * SFC)34 ZeroState(SymbolRef S, unsigned B, const StackFrameContext *SFC)
35 : ZeroSymbol(S), BlockID(B), SFC(SFC) {}
36
getStackFrameContext() const37 const StackFrameContext *getStackFrameContext() const { return SFC; }
38
operator ==(const ZeroState & X) const39 bool operator==(const ZeroState &X) const {
40 return BlockID == X.BlockID && SFC == X.SFC && ZeroSymbol == X.ZeroSymbol;
41 }
42
operator <(const ZeroState & X) const43 bool operator<(const ZeroState &X) const {
44 if (BlockID != X.BlockID)
45 return BlockID < X.BlockID;
46 if (SFC != X.SFC)
47 return SFC < X.SFC;
48 return ZeroSymbol < X.ZeroSymbol;
49 }
50
Profile(llvm::FoldingSetNodeID & ID) const51 void Profile(llvm::FoldingSetNodeID &ID) const {
52 ID.AddInteger(BlockID);
53 ID.AddPointer(SFC);
54 ID.AddPointer(ZeroSymbol);
55 }
56 };
57
58 class DivisionBRVisitor : public BugReporterVisitor {
59 private:
60 SymbolRef ZeroSymbol;
61 const StackFrameContext *SFC;
62 bool Satisfied;
63
64 public:
DivisionBRVisitor(SymbolRef ZeroSymbol,const StackFrameContext * SFC)65 DivisionBRVisitor(SymbolRef ZeroSymbol, const StackFrameContext *SFC)
66 : ZeroSymbol(ZeroSymbol), SFC(SFC), Satisfied(false) {}
67
Profile(llvm::FoldingSetNodeID & ID) const68 void Profile(llvm::FoldingSetNodeID &ID) const override {
69 ID.Add(ZeroSymbol);
70 ID.Add(SFC);
71 }
72
73 PathDiagnosticPieceRef VisitNode(const ExplodedNode *Succ,
74 BugReporterContext &BRC,
75 PathSensitiveBugReport &BR) override;
76 };
77
78 class TestAfterDivZeroChecker
79 : public Checker<check::PreStmt<BinaryOperator>, check::BranchCondition,
80 check::EndFunction> {
81 mutable std::unique_ptr<BuiltinBug> DivZeroBug;
82 void reportBug(SVal Val, CheckerContext &C) const;
83
84 public:
85 void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
86 void checkBranchCondition(const Stmt *Condition, CheckerContext &C) const;
87 void checkEndFunction(const ReturnStmt *RS, CheckerContext &C) const;
88 void setDivZeroMap(SVal Var, CheckerContext &C) const;
89 bool hasDivZeroMap(SVal Var, const CheckerContext &C) const;
90 bool isZero(SVal S, CheckerContext &C) const;
91 };
92 } // end anonymous namespace
93
REGISTER_SET_WITH_PROGRAMSTATE(DivZeroMap,ZeroState)94 REGISTER_SET_WITH_PROGRAMSTATE(DivZeroMap, ZeroState)
95
96 PathDiagnosticPieceRef
97 DivisionBRVisitor::VisitNode(const ExplodedNode *Succ, BugReporterContext &BRC,
98 PathSensitiveBugReport &BR) {
99 if (Satisfied)
100 return nullptr;
101
102 const Expr *E = nullptr;
103
104 if (std::optional<PostStmt> P = Succ->getLocationAs<PostStmt>())
105 if (const BinaryOperator *BO = P->getStmtAs<BinaryOperator>()) {
106 BinaryOperator::Opcode Op = BO->getOpcode();
107 if (Op == BO_Div || Op == BO_Rem || Op == BO_DivAssign ||
108 Op == BO_RemAssign) {
109 E = BO->getRHS();
110 }
111 }
112
113 if (!E)
114 return nullptr;
115
116 SVal S = Succ->getSVal(E);
117 if (ZeroSymbol == S.getAsSymbol() && SFC == Succ->getStackFrame()) {
118 Satisfied = true;
119
120 // Construct a new PathDiagnosticPiece.
121 ProgramPoint P = Succ->getLocation();
122 PathDiagnosticLocation L =
123 PathDiagnosticLocation::create(P, BRC.getSourceManager());
124
125 if (!L.isValid() || !L.asLocation().isValid())
126 return nullptr;
127
128 return std::make_shared<PathDiagnosticEventPiece>(
129 L, "Division with compared value made here");
130 }
131
132 return nullptr;
133 }
134
isZero(SVal S,CheckerContext & C) const135 bool TestAfterDivZeroChecker::isZero(SVal S, CheckerContext &C) const {
136 std::optional<DefinedSVal> DSV = S.getAs<DefinedSVal>();
137
138 if (!DSV)
139 return false;
140
141 ConstraintManager &CM = C.getConstraintManager();
142 return !CM.assume(C.getState(), *DSV, true);
143 }
144
setDivZeroMap(SVal Var,CheckerContext & C) const145 void TestAfterDivZeroChecker::setDivZeroMap(SVal Var, CheckerContext &C) const {
146 SymbolRef SR = Var.getAsSymbol();
147 if (!SR)
148 return;
149
150 ProgramStateRef State = C.getState();
151 State =
152 State->add<DivZeroMap>(ZeroState(SR, C.getBlockID(), C.getStackFrame()));
153 C.addTransition(State);
154 }
155
hasDivZeroMap(SVal Var,const CheckerContext & C) const156 bool TestAfterDivZeroChecker::hasDivZeroMap(SVal Var,
157 const CheckerContext &C) const {
158 SymbolRef SR = Var.getAsSymbol();
159 if (!SR)
160 return false;
161
162 ZeroState ZS(SR, C.getBlockID(), C.getStackFrame());
163 return C.getState()->contains<DivZeroMap>(ZS);
164 }
165
reportBug(SVal Val,CheckerContext & C) const166 void TestAfterDivZeroChecker::reportBug(SVal Val, CheckerContext &C) const {
167 if (ExplodedNode *N = C.generateErrorNode(C.getState())) {
168 if (!DivZeroBug)
169 DivZeroBug.reset(new BuiltinBug(this, "Division by zero"));
170
171 auto R = std::make_unique<PathSensitiveBugReport>(
172 *DivZeroBug, "Value being compared against zero has already been used "
173 "for division",
174 N);
175
176 R->addVisitor(std::make_unique<DivisionBRVisitor>(Val.getAsSymbol(),
177 C.getStackFrame()));
178 C.emitReport(std::move(R));
179 }
180 }
181
checkEndFunction(const ReturnStmt *,CheckerContext & C) const182 void TestAfterDivZeroChecker::checkEndFunction(const ReturnStmt *,
183 CheckerContext &C) const {
184 ProgramStateRef State = C.getState();
185
186 DivZeroMapTy DivZeroes = State->get<DivZeroMap>();
187 if (DivZeroes.isEmpty())
188 return;
189
190 DivZeroMapTy::Factory &F = State->get_context<DivZeroMap>();
191 for (llvm::ImmutableSet<ZeroState>::iterator I = DivZeroes.begin(),
192 E = DivZeroes.end();
193 I != E; ++I) {
194 ZeroState ZS = *I;
195 if (ZS.getStackFrameContext() == C.getStackFrame())
196 DivZeroes = F.remove(DivZeroes, ZS);
197 }
198 C.addTransition(State->set<DivZeroMap>(DivZeroes));
199 }
200
checkPreStmt(const BinaryOperator * B,CheckerContext & C) const201 void TestAfterDivZeroChecker::checkPreStmt(const BinaryOperator *B,
202 CheckerContext &C) const {
203 BinaryOperator::Opcode Op = B->getOpcode();
204 if (Op == BO_Div || Op == BO_Rem || Op == BO_DivAssign ||
205 Op == BO_RemAssign) {
206 SVal S = C.getSVal(B->getRHS());
207
208 if (!isZero(S, C))
209 setDivZeroMap(S, C);
210 }
211 }
212
checkBranchCondition(const Stmt * Condition,CheckerContext & C) const213 void TestAfterDivZeroChecker::checkBranchCondition(const Stmt *Condition,
214 CheckerContext &C) const {
215 if (const BinaryOperator *B = dyn_cast<BinaryOperator>(Condition)) {
216 if (B->isComparisonOp()) {
217 const IntegerLiteral *IntLiteral = dyn_cast<IntegerLiteral>(B->getRHS());
218 bool LRHS = true;
219 if (!IntLiteral) {
220 IntLiteral = dyn_cast<IntegerLiteral>(B->getLHS());
221 LRHS = false;
222 }
223
224 if (!IntLiteral || IntLiteral->getValue() != 0)
225 return;
226
227 SVal Val = C.getSVal(LRHS ? B->getLHS() : B->getRHS());
228 if (hasDivZeroMap(Val, C))
229 reportBug(Val, C);
230 }
231 } else if (const UnaryOperator *U = dyn_cast<UnaryOperator>(Condition)) {
232 if (U->getOpcode() == UO_LNot) {
233 SVal Val;
234 if (const ImplicitCastExpr *I =
235 dyn_cast<ImplicitCastExpr>(U->getSubExpr()))
236 Val = C.getSVal(I->getSubExpr());
237
238 if (hasDivZeroMap(Val, C))
239 reportBug(Val, C);
240 else {
241 Val = C.getSVal(U->getSubExpr());
242 if (hasDivZeroMap(Val, C))
243 reportBug(Val, C);
244 }
245 }
246 } else if (const ImplicitCastExpr *IE =
247 dyn_cast<ImplicitCastExpr>(Condition)) {
248 SVal Val = C.getSVal(IE->getSubExpr());
249
250 if (hasDivZeroMap(Val, C))
251 reportBug(Val, C);
252 else {
253 SVal Val = C.getSVal(Condition);
254
255 if (hasDivZeroMap(Val, C))
256 reportBug(Val, C);
257 }
258 }
259 }
260
registerTestAfterDivZeroChecker(CheckerManager & mgr)261 void ento::registerTestAfterDivZeroChecker(CheckerManager &mgr) {
262 mgr.registerChecker<TestAfterDivZeroChecker>();
263 }
264
shouldRegisterTestAfterDivZeroChecker(const CheckerManager & mgr)265 bool ento::shouldRegisterTestAfterDivZeroChecker(const CheckerManager &mgr) {
266 return true;
267 }
268